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I am trying to cut out the rebel alliance symbol from a hollow half sphere the size of a golfball to 3D print a golf ball marking stencil. I tried this with tinkercad and already printed it successfully like this: Initial try for my marking stencil with a cut straight down As you can see, I simply extruded an svg and cut out straight down. This works somehow, but of course it is a straight cut, which especially on the outer curve produces quite an angled border compared to the normal of the golf ball, which makes painting the edges harder than it could be.

Now I wanted to bend the symbol along the normals of the sphere curvature using blender and a technique I found here: https://blender.stackexchange.com/a/115121/116795 , bind object with SurfaceDeform modifier to plane, bind Plane with shrinkwrap to Sphere. And it worked, but it somehow looks ragged especially on the inner curvature:

ragged inner edges on the curvature

I have played around with the modifier settings like an offset for the shrinkwrap, increasing subdivision, even using the Remesh Modifier to get a different distribution of vertices along the edges. But nothing was really clean.

Basically what I would really want is to extrude an arbitrary svg along the normals of a sphere - in my imagination this should deliver the cleanest result.

So any tips to improve the quality of the edge curvature or pointers to a completely different technique would be highly appreciated, thank you!

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    $\begingroup$ Simpler to cut a hole into the single-skin sphere, and then rely on a Solidify modifier to give you the thickness-along-normals $\endgroup$ Feb 12 '21 at 10:02
  • $\begingroup$ That is a very good idea @RobinBetts, I didn't think about that, thank you! I'll try this and return with my findings. $\endgroup$ Feb 12 '21 at 14:48
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I tried the suggested Solidify on a single-skin sphere, but I didn't manage to get the result I wanted. But I worked out a similar approach - with a little more work and without modifiers, that did the trick:

  1. Create Sphere of approriate size
  2. Use Boolean to cut off lower half to get to the desired half sphere and cut out the desired SVG symbol as I did before
  3. Use "Edit Mode" to remove all inner vertices created by the booleans to produce a single skin sphere with cutout as suggested by Robin. Singleskin with cutout removed
  4. Duplicate the object, scale it so there is a second, slightly larger version of it - as desired for the thickness
  5. Join the two objects and "stitch" the edges with CTRL-E - "Bridge Edge loops"

I had to select the inner cutouts manually, "select loop" didn't work there. But in the end, the result was worth the effort: Final result

Thanks for your help, I hope somebody finds this useful!

UPDATE: I also found out why the solidify didn't work before, I didn't actually use a singleskin sphere (Step 3 from above), but instead I used a boolean operation to cut out the inner side with an only slightly smaller sphere. Which LOOKED single, but actually was a normal doubleskinned sphere. With the singleskinned sphere, it worked like a charm. So, thanks again Robin for the suggestion, you were spot on, if only I had done it right in the first place, this would have worked perfectly!

So, alternative to my more time-intensive method:

  1. Create Sphere of approriate size
  2. Use Boolean to cut off lower half to get to the desired half sphere and cut out the desired SVG symbol as I did before
  3. Use "Edit Mode" to remove all inner vertices created by the booleans to produce a single skin sphere with cutout as suggested by Robin.
  4. Switch back to "Object Mode" and use the Solidify modifier to get the desired effect with a lot less effort :).

Update 2: Yep, it works :) use on a golf ball (left), Printing result (right)

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    $\begingroup$ Nice clean result!.. Surprised you didn't have a nightmare cleaning up after the boolean ! $\endgroup$ Feb 13 '21 at 22:24
  • $\begingroup$ No, actually the cleanup was done rather quickly, might be because the base cut with the solidified svg was also rather clean. Printer is already on it so I can show off the end result of all this later :). $\endgroup$ Feb 13 '21 at 22:58

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